Investigation on Grain Size Effect of Rolling Texture in Copper

Cold rolling (CR) was conducted on coarse grained (CG) and ultrafine-grained (UFG) coppers, obtained by 1 and 8 passes in the equal channel angel pressing (ECAP), to investigate the effect of grain size on rolling texture. The microstructure was refined to UFG (~420 nm) with the ECAP pass increased to 8, while only band-like CG microstructure was observed in the 1 pass processed copper. The influence of the texture before CR could be excluded as the crystallographic texture kept similar for different ECAP pass. Pole figures (PFs) showed that the shear texture introduced by ECAP was replaced by rolling texture after CR. Furthermore, the rolling texture was a kind of classical copper-type for the CG copper, while a brass-type rolling texture was observed in the UFG copper. TEM results confirmed that the deformation nanotwins were only observed in the UFG copper, while the microstructure of CG copper was further compressed and subdivided. It indicated that the observed differences in rolling texture component and density might be contributed to the grain size effect which resulted in different deformation mechanism and grain subdivision behavior.

Effect of Extrusion Route on Grain Refinement during ECAP Process

The effect of the extrusion route (A, C and BC) on grain refinement during ECAP process in 99.9995% (5N5) high pure aluminum using a die with a channel-intersection angle 90° was investigated. It was found through experiment that, the grain was very coarse in the cast ingot of 5N5 high pure aluminum, and the average grain size is about 50~60mm. After two ECAP passes, the average grain size is 300μm, 550μm and 200μm respectively with the extrusion route of Route A, C and BC. After eight ECAP passes, the average grain size is 100μm, 100μm and 30μm respectively with the extrusion route of Route A, C and BC. It indicates that the route BCis more effective than Route A and C. TEM micrograph of 5N5 high pure Al with different ECAP pass under Route BCwas studied.

Mechanical Properties and Microstructure Development of Ultrafine-Grained Cu Processed by ECAP

Technical purity Cu (99.95 wt%) polycrystals have been processed at room temperature by equal channel angular pressing. The results of mechanical tests and the microstructure characterization by various experimental techniques are presented. The yield stress as well as the strength were shown to increase with increasing strain and exceed the respective values of a coarsegrained material. The microstructure development and its fragmentation after ECAP was investigated by the TEM and EBSD. The proportion of high angle grain boundaries was found to increase with increasing strain reaching the value of 90% after 8 ECAP passes. Two kinds of defects were identified in ECAP specimens by positron annihilation spectrometry (PAS): (a) dislocations which represent the dominant kind of defects, and (b) small vacancy clusters (so called microvoids). The main increase of defect density was found to occur during the first ECAP pass. PAS analysis indicated that in the specimens subjected to one ECAP pass the mean dislocation density ρD and the concentration of microvoids cν exceeded the values of 1014 m-2 and 10-4 at.-1, respectively. After 4 passes, the number of defects becomes saturated and practically does not change with increasing strain.

Crystallographic Texture Development in CP Ti Subjected to ECAP

In this article we present the results of the experimental research and those of the processes developing the crystallographic texture of computer modeling in CP Ti in the process of 1-4 equal channel angular pressing (ECAP) passes along the route ВС. The goal of the research was to determine the active deformation mechanisms, depending on the strain degree, accumulated in the ECAP process. The research was carried out by the method of X-ray analysis and by computer modeling. Computer modeling was carried out on the example of visco-plastic self-consistent model. Thereby, the basal, the prismatic and the pyramidal (of the 1st and of the 2nd order) slip systems were considered as possible active slip systems. Besides, the possibility of activating the tensile and the compressive twinning systems were taken into consideration. As the result of the carried out experimental research, the objective laws of forming preferred orientations were determined. For the first time, with the help of computer modeling, made up to the 4th ECAP pass, it was shown that the crystallographic texture development processes in CP Ti in ECAP, realized at temperature of 723 K, can be explained by activation of the basal, prismatic and pyramidal (of the 1st order) slip systems and compressive twinning systems. Therefore, the increase of the ECAP passes can lead to amplification of contribution of the basal and prismatic slip systems, as well as the insignificant weakening of the contribution of pyramidal slip systems (of the 1st order). Moreover, the compressive twinning can become obvious only in the 1st ECAP pass.

Corrosion and Mechanical Behaviors of Cu-35%Zn Alloy Prepared by Equal Channel Angular Pressing (ECAP)

Effect of equal-channel angular pressing (ECAP) on the corrosion and mechanical properties of Cu-35%Zn alloy were studied. Two types of feed direction were selected. One is parallel pass and the other is 180°degree rotated ECAP pass after each pass. Both ECAP passes made texture in each specimen in which shear band with 45 degree on transverse direction and twins exist. The specimen prepared by parallel ECAP pass has finer shear band. Relative amount of twins to shear band on the microstructure becomes decrease with number of ECAP pass. Microhardness increased from 75 Hv to 210 Hv by ECAP. The corrosion potential and rate of the ECAPed Cu-35%Zn alloys in aerated aqueous 1 M-H2SO4 solution were –92.3 mVSHE and 3.72x10-2 A/cm2 for route- A and –38.6 mVSHE and 5.08x10-2 A/cm2 for route-C, respectively. The corrosion potential and rate of depended on the feed direction and number of pass.

An EBSD Study of Texture and Grain Boundary Evolution in a Strongly Textured Aluminium Alloy during ECA Pressing

The texture and grain boundary evolution during equal channel angular pressing (ECAP) of a spray-cast Al-7034 (Al-Zn-Mg-Cu) alloy containing intermetallic particles with a range of sizes was studied through electron backscatter diffraction (EBSD). Up to 8 passes of ECAP using route Bc were employed. The initial ECAP pass leads to the development of low angle grain boundaries and subsequent passes lead to a relatively rapid increase in the fraction of high angle grain boundaries. Before ECAP, the material possessed a strong <111> and <100> fibre texture. On ECAP, the <111> fibre texture component is mostly retained but the <100> fibre develops to a Cube texture after the first ECAP pass. Goss textures form from about 4 passes of ECAP.